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Posts Tagged ‘Canis’

African golden wolf

What we do know about the origins of Canis species is much more hotly-contested than what we know about the evolution of our own species. The earliest fossils of the genus are roughly 6 million years old, and the oldest species in the “wolf lineage” is Canis lepophagus, which lived in the American Southwest and Northern Mexico 5 million years ago.  This species is often posited as the direct ancestor of the coyote, and it may have been a direct ancestor of all the entire wolf-like canid lineage.

Of course, recent discoveries that have come from full genome comparisons make things a little complicated. With the discovery that coyotes diverged from gray wolves as recently as 50,000 years ago, the linear evolution from Canis lepophagus to Canis latrans is probably invalid.  Further another full genome study that used a single Israeli golden jackal (Canis aureus) as the outgrouping sample to determine when dogs and gray wolves split, revealed that this particular jackal diverged from gray wolves less than 400,000 years ago.

Both of these dates are far more recent that the millions of years that are assumed to separate these wolf-like canids from each other. Of course, more work must be done. We need more studies on coyote genomes, but these researchers have come across what could be the most important discovery in our understanding of the evolution of Canis species. Depending upon the study, coyotes and gray wolves were thought to have diverged between 700,000 to 1 million years ago, and this assumption is used to calculate when other Canis have diverged.

Now, this assumption always did bother me, because if Canis lepophagus leads directly to Canis latrans, where do wolves fit in?  Because in order for that model to work, gray wolves have to evolve from a very small coyote-like ancestor with very few transitions in between. It always just seemed to me like it was unworkable.

Further, there is a whole host of literature on the evolution of gray wolves in Eurasia, and in most European literature, there is a general acceptance of how gray wolves evolved from a smaller wolf called Canis mosbachensis.

Wolfgang Soergel, a German paleontologist at the University of Tübingen, discovered Canis mosbachensis at a site near Jockgrim in 1925. The animal is sometimes called the “Mosbach wolf,” which means it was found in the Mosbach Sands, where many fossils from the Middle Pleistocene have been found.

Mark Derr was particularly interested in this species in his How the Dog Became the Dog.  He points out that the earliest dated fossils of this species are 1.5 million years old and come from the ‘Ubeidiya excavations in Israel.  The most recent Canis mosbachensis remains in Europe are about 400,000 years old, after which time they were replaced by Canis lupus.  Derr speculated about the relationship mosbachensis might have had with early hominin species, which were also well-known from that site, and suggested that they might had some kind of relationship.

Further, there is a growing tendency among paleontologists to group Canis mosbachensis with another wolf that was its contemporary. This wolf, called Canis variabilis, was discovered at the Zhoukoudian Cave System in China in 1934. Its discoverer was Pei Wenzhong, who became respected paleontologist, archaeologist, and anthropologist in the People’s Republic of China. It was a small wolf with a proportionally smaller brain, and it has long been a subject of great speculation.

And this speculation tends to get lots of attention, for this cave system is much more famous for the discovery of a type of Homo erectus called “Peking Man.”  It is particularly popular among the people who insist that dogs are not wolves, which is about as scientifically untenable as the “birds are not dinosaurs” (BAND) clique of scholarship.

Mark Derr and as well as more established scholarship have begun to group variabilis and mosbachensis together. Variablis has also been found in Yakutia, and it may have been that varibablis nothing more than an East Asian variant of mosbachensis.

These wolves were not large animals. They varied from the size of an Eastern coyote to the size of an Indian wolf. They were not the top dogs of the Eurasian predator guild.

Indeed, they played second fiddle to a larger pack-hunting canid called Xenocyon lycaonoides, a large species that is sometimes considered ancestral to the African wild dog and the dhole, but the recent discovery of Lycaon sekoweiwhich was a much more likely ancestor of the African wild dog, suggests that it was more likely a sister species to that lineage.

Although canids resembling Canis lupus have been found in Alaska and Siberia that date to 800,000 years ago, anatomically modern wolves are not confirmed in the Eurasian faunal guild until 300,000-500,000 years before present.

I’m throwing a lot of dates at you right now, because if the modern Canis lupus species is as recent as the current scholarship suggests, then we can sort of begin to piece together how the entire genus evolved.

And we’re helped by the fact that we have an ancient DNA study on a Yakutian “Canis variablis” specimen. This specimen would have been among the latest of its species, for it has been dated to 360,000 years before present. Parts of its ancient mitochondrial DNA has been compared to other sequences from ancient wolves, and it has indeed confirmed that this animal is related to the lineage that leads to wolves and domestic dogs.  The paper detailing its findings suggests that there is a direct linkage between this specimen and modern dog lineages, but one must be careful in interpreting too much from limited mitochondrial DNA studies.

360,000 years ago is not that far from the proposed divergence between gray wolves and the Israel golden jackal in genome comparison study I mentioned at the beginning of the post.

This really could suggest something a bit controversial and bold. It make take some time for all this to be tested, but it is a hypothesis worth considering.

I suggest that all this evidence shows that Canis mosbachensis is the ancestor of all interfertile Canis, with the possible exception of the Ethiopian wolf.

If the Ethiopian wolf is not descended from that species, then it is a sister taxon. It is not really clear how divergent Ethiopian wolves are from the rest of interfertile Canis, but their divergence estimates currently suggest that it diverged from the rest of the wolf-like clade 1.6 million years ago, which is just before Canis mosbachensis appears in the fossil record.

If that more recent date holds for the split for the Eurasian golden jackal, then it is almost certain that this hypothesis is correct.  The Eurasian golden jackal may be nothing more than a sister species to a great species complex that includes the coyote, gray wolf, dingo, and domestic dog that both derived from divergent populations of Canis mosbachensis. 

The exact position of the Himalayan wolf and the African golden wolf are still not clear. We do know, though, that both are more closely related to the coyote and gray wolf than the Eurasian golden jackal is, and if its split from the gray wolf is a recent as less than 400,000 years ago, then it is very likely that all of these animals are more closely related to the main Holarctic population of gray wolves than we have assumed.

The recent divergence of all these Canis species is why there is so much interfertility among them.

And if these animals are as recently divergent as is inferred, their exact species status is going to be questioned.

And really should be, at least from a simple cladistics perspective.

More work does need to be done, but I don’t think my hypothesis is too radical.

It just seems that this is a possibility that could explored.

 

 

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brush wolf

It cannot be overstated how much the discovery that coyotes are not as distantly related to wolves as we believed ultimately questions our entire understanding of the evolution of the Canis species.

The traditional understanding Canis species evolved from some form of Eucyon dog some six million years ago. Wang and Tedford, who wrote the most important book on the paleontology of the dog family, believe this was Eucyon davisi, which was the first of its genus to enter Eurasia. The genus Eucyon is where the common ancestor of the Canis dogs (including Lycaon and Cuon) and the South American wild dogs would be located. Eucyon dogs were small. Imagine them as being something like a black-backed jackal or a Hoary fox rather than a coyote.

Then, 5 million years later in the Southwestern US and northern Mexico, a coyote-like Canis evolved, which was called Canis lepophagus. This animal is sometimes considered the common ancestor of wolves and coyotes. It may be, but considering how close we now know wolves and coyotes are now, it’s not the most recent common ancestor. Canis lepophagus did migrate into Eurasia, where it either founded or is identical to Canis arnensis.

In Eurasia, several smaller jackal-to-coyote forms evolved. One of these was Canis estruscus,  which then evolved into Canis mosbachensis (which is called Canis variabilis in China).

Ron Nowak believed the red wolf was an offshoot of this wolf that wound up colonizing North America and then becoming isolated from the rest of Canis mobachensis when the ice sheets expanded. There was also a competing view that the red wolf was actually a remnant version of Canis edwardii or Canis priscolatrans (which were probably the same animal). This animal was roughly the size of a red wolf, but Nowak rejected it as a red wolf ancestor because it lived too early for what he thought were red wolf fossils.

The Eurasian wolf species evolved mosbachensis-variabilis, but the two forms of wolf shared habitat and likely exchanged genes, making it very difficult

The coyote’s evolution was never clear. It was thought to have evolved out of Canis lepophagus. It was thought that lepophagus evolved into edwardii, and then it began to become more gracile and smaller, eventually becoming the now coyote.  It’s now pretty clear that it evolved out of the Eurasian Canis lupus and not these endemic North American “wolves.”

It either evolved from the modern wolf, which evolved into roughly its current form 800,000 years ago, or it came from a late surviving mosbachensis-type wolves that were regularly crossing with modern wolves before they came into this continent. Maybe the remains that Nowak had been considering “red wolves,” were actually these ancestral wolves that were evolving into the modern coyote.

Maybe when this wave of wolves came back across from Eurasia, perhaps 50,000-100,000 years ago, it came into a world already dominated by a dire wolves, which already occupied the niche for large, pack hunting canids and this wave of Canis lupus evolved as the American jackal.  After all, the bobcat is just a diminutive Eurasian lynx that found itself in a very similar position when it came into this continent, and it evolved to be a smaller animal that generally hunts smaller quarry than its larger ancestor. Of course, the modern bobcat didn’t reach its current form until about 20,000 years ago, but it still was forced to adapt to a slightly different niche than its Eurasian ancestor.

In literature on the paleontology of Canis, there is a heated debate as to how these animals all fit. The conventional view is that the wolf evolved from Canis mosbachensis/variabilis through Canis etruscus, which may be the same thing as Canis edwardii/ Canis priscolatrans. Wang and Tedford contend that the coyote and wolf split from Eucyon.  The modern wolf evolved from Canis chihliensis, which was a large wolf-like canid. It spread into North America to found Canis armbrusteri, which then evolved into the dire wolf (Canis dirus) in North America and Canis gezi and Canis nehringi in South America.  In the Old World, another offshoot of chihliensis gave rise to Canis falconeri, which the supposedly gave rise to the Xencyon, which is supposed ancestor of the dhole and African wild dog. Another view holds that the Armbruster’s wolf (C armbrusteri) is descended from edwardii/priscolatrans (which may be the same as etruscus). This lineage then gave rise to the dire wolf and the two sister species in South America, thus descending solely from North America wolves.

All of these ideas come from paleontology, and they pretty much are done without looking very deeply into the studies that are examining the DNA of these species. It is pretty obvious from that literature that the notion that coyotes and wolves split at the time of the Eucyon ancestor is quite wrong. For that hypothesis to work, African of  wild dogs and dholes would have to be genetically closer to wolves than coyotes and golden jackals are. They aren’t.

But if the genome-wide analysis shows that coyotes are so much more closely related to wolves is true, then all these fossil and subfossil canids that are said to be the most recent common ancestor of wolves and coyotes simply aren’t.  Instead, all of these species that are classified in Canis are likely a mix of evolutionary dead ends, like the dire and Armbruster’s wolf, or could be hidden ancestors of extant canids that aren’t wolves or coyotes.

For example, black-backed and side-striped jackals diverged from the rest of Canis and its allies at about the same time that Eucyon was diverging from Canis. It is possible that there are many relatives of these particular dogs that are hidden in this vast sea of Canis fossils.

The new discovery about the coyote’s split from the wolf also means that any remains of North American canid that are listed as coyote that date to 1 million years before present are not coyotes. What they actually were is a very good question.

We’ve spent a lot of time assuming that coyotes and wolves were quite divergent. We know now that they really aren’t, but when we look into the past at all the “wolves” and “coyotes” that came before, we see how this genus became so successful. It can easily evolve into big game-hunting forms, but the real success is in its ability to assume the size and shape of the generalist predator. Phenotypic plasticity is a wonderful thing for a lineage to possess.

But the real message of the new discovery about wolves and coyotes should be is a cautionary tale about paleontology. Paleontology is a wonderful science, and it makes amazing discoveries every day, but when its faced with a lineage of animals where phenotypic plasticity and tendencies toward parallel and convergent evolution are commonplace, it is bound to make errors. Paleontologists aren’t examining flesh and blood that can have its molecules tested for relationships. They are measuring anatomical characters and determining phylogenetic relationships based upon the similarities of these characters.

Which works well.

Until you get something like wolves and coyotes, where there are many ancient fossil and subfossil remains that look like they could be ancestors of either.

But the DNA says they aren’t.

And paleontology would have problem catching the inverse. There are many species that we’ve discovered only through DNA testing. African butterfly fish in the Congo and Niger basins look identical to each other, but they have been isolated from each other for 57 million years. I have yet to see this species split into two, but if they were mammals, you could bet they would be placed in distinct species in heartbeat.

Paleontology is missing some really important things we’ve since found out through molecular analyses.

And paleontologists know this.

They are working with the data they have, and by definition, it’s going to be more incomplete than genetic studies.

Science is provisional. Different disciplines and methodologies are going to come up with different answers. It’s pretty amazing that one genome-wide assay study can wipe out so much literature in paleontology.

These debates have been raging for years.

And it turns out that everyone was actually wrong.

Update 21 August 2016:  It turns out that I missed a paper that actually did some limited DNA analysis and found that Canis nehringi was pretty much a South American dire wolf, as in it was likely the same species as the North American dire wolf. Canis gezi, however, was  more closely related to the modern maned wolf and had been incorrectly identified as a wolf. So let this stand as a correction to the error above.

 

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Eucyon and the wolf

The likely ancestor of all extant species of Canis and probably the dhole and African wild dog is featured in this print.

The smaller canid featured here is Eucyon, a type of canid that lived in North America during the Late Miocene (10-5 million years ago). Eucyon is  both the genus and common name for these canids, which weighed about 20 pounds.

Eucyon means “original dog,” and it believed that all the extant Canis and possible Canis species evolved from some sort Eucyon species around 6 million years ago.

The oldest extant Canis species is the black-backed jackal (C. meslmelas) of Southern and East Africa. Mitochondrial DNA studies suggest that it split off the Canis lineage between 2.5 and 4.5 million years ago.

I have seen depictions of Eucyons that show them looking a lot like black-backed jackals.

However, black-backed jackals are still quite derived from this ancestor, and from my reading of the literature, this depiction is more accurate.  The morphology of this animal is believed to have been very similar to a crab-eating fox, which isn’t actually a fox.

For most of the dog family’s history on this planet,North America was the main center for their evolution. Canis came from North America and then spread throughout Eurasia and Africa.  The dire wolf eventually colonized South America, and then through the domestic dog, the genus eventually spread virtually every else.

Yes. Dogs are much more American than any of us African great apes!

 

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A side-striped jackal (Canis adustus), the jackal no one talks about.

We’ve always called the smaller wild dogs in the genus Canis jackals.

Historically, there were four species of jackal:  the golden (Canis aureus), the black-backed (Canis mesomelas), the side-striped (Canis adustus), and the Simien (Canis simensis).

Some authorities considered they coyote (Canis latrans) to be a jackal, usually called “the American jackal.”

At one time, they were all placed in the genus Thous.

This, of course, assumed that these animals were all closely related to each other.

However, as we’ve looked at DNA analysis, the relationship between jackals shows that the term “jackal” is actually quite meaningless.

In 1994, an mtDNA study revealed that the Simien jackal had certain mtDNA sequences that were more similar to wolves than other jackals. It was thought to be a relict population of primitive wolves that came into Africa during the Pleistocene.

And from that time forth, the English name of this species was change to “Ethiopian wolf.”  I don’t call it anything else.

However, as more work was performed on jackals, certain facts became evident.

Initial studies of black-backed, side-striped, and golden jackal mtDNA revealed that black-backs in East Africa had huge variances in their mtDNA. Golden jackals had mtDNA that was most similar to coyotes and wolves, while black backs and side-stripes were more similar to each other.

And then the phylogeny of the dog family was drawn from a high-quality sequencing of the dog genome revealed that golden jackals were much more closely related to coyotes and the wolf and domestic dog species than the Ethiopian wolf was. We still call them Ethiopian wolves, even though golden jackals are more closely related to actual wolves than those animals are.

The other issue revealed through this research was that Canis, as it is traditionally classified, is a paraphyletic genus. Modern taxonomy is generally concerned with classifying animals according clades. Clades are, by definition monophyletic. That is, they contain all the animals that descend from a particular lineage.

The dog genome research revealed that two species that are never traditionally classified as being part of Canis, the African wild (Lycaon pictus) and the dhole (Cuon alpinus), actually should be included there.  It turns out that black-backed and side-striped jackals are more distantly related to the rest of Canis than these two species are.

And if we classify Canis with all the jackals, the Ethiopian wolf, and  the wolf and dog species and leave out the dhole and African wild dog, we’ve created a paraphyletic genus that is not useful to modern taxonomy.

Some have suggested giving the two endemic African jackals their own genus.

And this would make Canis monophyletic without including the African wild dog and dhole.

However, the genus that would remain would include several species that are all chemically interfertile with each other (at least in theory). Species complexes exist throughout that part of the Canis, and delineating species is very difficult the species in this lineage.

Although Robert Wayne at UCLA has suggested that black-backed and side-striped jackals might be able to interbreed, no one has confirmed a hybrid between these two species. African wild dogs might be able to hybridize with dholes, but because they live on different continents and because they are both fairly endangered, no one has attempted to cross them. (There are persistent rumors that dholes can cross with domestic dogs. One dog breed, the Bangkaew dog from Thailand, is said to have derived from a dog/dhole cross. However, I don’t believe this claim has ever been tested through DNA analysis.)

All this research has revealed that how we have traditionally thought about the dog family is probably wrong.

The golden jackal is actually a primitive offshoot of the wolf lineage, just as the coyote in the New World is. The Ethiopian wolf is an even more primitive offshoot.

The two endemic African jackals are the two oldest living species in the Canis lineage. They are even more distinct from this lineage than dholes and African wild dogs are.

We do not have a good replacement word for jackal.

I’ve suggested that we call golden jackals “Old World coyotes” almost as a joke.

But I don’t have a good name for either of the two remaining jackal.

Because black-backed jackals are so scrappy, I’ve even suggested that we call them “wild Jack Russells.”

Whatever we call them, the term jackal, if it’s used to reflect close relationships between species, is utterly meaningless.

With the exception of the two found only Africa, it doesn’t refer to any animals that have a close relationship with each other.

It’s just a term we use for smaller wild dogs that are in some way related to wolves.

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This phylogenetic tree comes from a study that used a high quality draft genome sequence of the domestic dog to make important comparisons within domestic dog breeds and also to make some comparisons with their relatives.

One of the most interesting discoveries in the this study was that the genus Canis as it is currently classified is paraphyletic.

Paraphyly is a major problem in cladistic taxonomy, for the goal is to have genera, orders, and families all to reflect common ancestry.

But if one looks at the species currently classified as belonging to the genus Canis on this phylogenetic tree, there is a gap between the two endemic African jackals– the side-striped (Canis adustus) and black-backed (Canis mesomelas)– and the other species in the genus Canis– the Ethiopian wolf (Canis simensis), the golden jackal (Canis aureus), the coyote (Canis latrans), and the Holarctic wolf/domestic dog/dingo/New Guinea singing dog species (Canis lupus). This clade of Canis  includes the interfertile Canis, where hybridization is possible between all members.

The two endemic African jackals cannot cross with any other members of the genus. Let me repeat that:  there are no black-backed jackal or side-striped jackal hybrids with domestic dogs or any other dog species. Some people claim that pariah and village dogs from Africa have ancestry from these jackals, but no genetic evidence has been provided to confirm the existence of these hybrids.

If one follows that phylogenetic tree, the gap between the two groups of Canis is filled with two species. These are the so-called “hunting dogs,”  which we call the dhole (Cuon alpinus) and the African wild dog (Lycaon pictus). The most common hypothesis about the origin of these dogs is they are both derivatives of an extinct wolf-like dog that was called Xenocyon lycaonoides. There is some debate about whether both of these dog descend from them, but the bulk of the literature suggests that they derive from this species.  Xenocyon filled the same ecological niche as wolves eventually did, but it was not part of the wolf lineage.

The conventional thinking on Xenocyon is that it evolved into the dhole and African wild dog species, but there is at least one study that suggests that the African wild dog derived from a different lineage. I am a bit skeptical of this study because it was based upon tooth morphology. Tooth morphology is one aspect that has led us to believe that African wild dogs and dholes are related, but one should keep in mind that tooth morphology once led us to believe that dholes and African wild dogs were closely related to the South American bush dog (Speothos venaticus), which we now know is part of the South American canid clade.  If these tooth adaptations can evolve from that such disparate lineages, I don’t see why they couldn’t have evolved from unrelated lineages in the past.

Whatever the exact ancestors of the dhole and the African wild dog, they create a gap in the phylogenetic tree between the interfertile Canis and the endemic African jackals.

That means that we have to make Canis monophyletic.

The easiest way to do this is to get rid of the genera Cuon and Lycaon.   The African wild dog becomes Canis pictus (the painted dog) and the dhole become Canis alpinus (the mountain dog).  I don’t recommend going with Canis lycaon to denote the African wild dog. This name has been bandied about for the proposed but now largely falsified Eastern wolf species, and using this name for the African wild dog would just make things very confusing.

If Cuon and Lycaon are no longer unique genera and the species within them are reclassifed as Canis, the entire genus becomes monophyletic.

I would recommend this recourse.

However, one could keep Cuon and Lycaon if one created a unique genus for the black-backed and side-striped jackals. Several genus names have been proposed for jackals, but I don’t know if we have a good system for coming up with one. The study that suggests that Xenocyon and the African wild dog suggests that we use the Lupulella for these two jackals, which would connect with what have been called primitive jackals that were living in Northwestern Africa during the Pleistocene. These primitive jackals had morphology that was very similar to the modern raccoon dog (Nyctereutes procyonoides). Black-backed jackals in their current form trace to the early Pleistocene in East Africa, so they likely didn’t derive from these primitive ones in Northwest Africa. And it is unlikely that side-striped jackals evolved from them either, for it is a newer species than the black-backed jackal and is usually considered a sister species with the black-backed jackal. Indeed, it is also possible that side-striped jackals derived from black-backed jackals that were adapted to living in dense forests.

The skull morphology of the ancient Lupulella suggests that it may not have been a jackal at all, but it may have been a dog derived from the raccoon dog lineage that just happened to have some features in common with modern jackals.

Raccoon dogs and bat-eared foxes are currently considered basal foxes.  At one time, they were both considered basal to the entire dog family, but now the only odd-ball basal canid species are the gray foxes in the genus Urocyon. It is at least as likely that the extinct Lupulella species were jackal-like derivatives of the raccoon dog lineage, and combining modern black-backed and side-striped jackals with these species is not well-advised.

Therefore, the best course of action is to move the African wild dog and the  dhole into Canis.

However, I do think we need to create subgenera within Canis to denote phylogenetic relationships. These subgenera should create three clades: one for the interfertile Canis, one for the hunting dogs, and one for the two endemic African jackals.

This is perhaps the best way to do away with a clumsy paraphyletic genus.

And one should understand that the genus Canis is not the only paraphyletic clade in zoology. The truth is we have lots to figure out about the exact evolutionary relationships that exist between different species.  There are some species, like the South American red brocket deer (Mazama sp.), that likely contain several different species from very distinct evolutionary lineages that have been combined within the same species based upon nothing more than superficial reasons.

With Canis, fixing this problem is pretty easy. However, it might be difficult to get the scientific names changed to reflect phylogeny properly.

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